In addition to the display of broadcast television programming, television receivers often provide a monitor capability for the display video or graphical material from other signal sources such as DVD players, computers and computer games. The bandwidth of these non-broadcast signals may vary from 3.5 MHz for a VCR derived video signal, to the region of 25 MHz for computer generated images. The power consumption of a video output amplifier in the TV monitor display increases with the bandwidth required to faithfully display the non-broadcast signal bandwidth and amplitude. Modern TV displays frequently display signals from different sources often with different content bandwidths. Typically an average power dissipation in a simple class-A video amplifier with a bandwidth in a range from 5 MHz to 20 MHz will correspondingly dissipate between 2W to 5W. However, in a high bandwidth active load amplifier this can easily exceed 5 Watts. Because a cathode ray tube receiver monitor contains three video output amplifiers these can represent a significant contribution to the total power consumption of the display.
It is known to control an operating point of a video amplifier by means of feedback from a current path which undergoes a parameter change as a consequence of operation at increasing frequencies. The feedback signal can be developed across an emitter resistor in proportion to the current which increases at higher frequencies. The feedback signal is filtered and applied to the amplifier input to influence the operating point.
To reduce levels of unintentional emissions it is known to analyze the spectral content of a display signal and generate an emission control signal in accordance with input signals likely to cause emissions. Such a control signal can be applied to reduce subjective video peaking effects produced by scanning velocity modulation (SVM), or to dynamically modulate video peaking circuitry to diminish emissions. It can be appreciated that analysis of the spectral content of the display signal can provide an accurate indication of likely emission candidates, with the remedy being the dynamic reduction of image enhancement. However such dynamic enhancement control is unlike the objectives herein which adaptively control amplifier bandwidth to be sufficient for the actual display signal present at the amplifier input.
With increasing computer and video game usage plus 24 hour broadcast or cable programming availability, television receiver monitors can be operational for extended periods of time, hence it would be beneficial in terms of device reliability and energy consumption to reduce the power dissipated by the display.